Resonance cells for optical pumping



March 22, 1966 MALNAR 3,242,423

RESONANCE CELLS FOR OPTICAL PUMPING Filed Jan. 9, 1963 United States Patent 3 242 423 RESGNANCE CELLS F0 R OPTICAL PUMPING Lon Malnar, Paris, France, assignor to C.S.F.Compagnie gnrale de tlgraphie Sans Fil, a corporation of The present invention relates to resonance cells for optical pumping. Such cells may be used in many applications, for example in certain magnetometers. They may comprise a glass or Pyrex vessel containing an alkali metal, such as cesium or rubidium, and saturated vapour of this metal and, in a magnetometer, the vapour is subjected to the action of a uniform magnetic field.

Under the action of an optical pump the population of excited atoms, the magnetic moment of which is parallel to the magnetic field applied, increases.

However, known cells of this type have a major drawback.

The saturated vapour is at a low pressure and the mean free path of the atom is greater than the dimensions of the vessel. The vapour atoms are subjected to a large number of impacts against the wall, resulting in the destruction of the favourable orientation due to optical pumping.

To eliminate this drawback, a rare gas, such as argon, may be introduced into the vessel at a pressure higher than that of the vapour, or else the walls of the vessel may be coated with a layer of parafiin or silicone against which the atoms may be rebound without changing their orientation.

This layer has to be very thin, so as to maintain the transparency of the vessel to the light from the optical pump and this makes it difficult to coat certain portions of the vessel, for example the pumping stem, with the protecting layer.

In addition, the collision of the atoms of the gaseous metal against the solid metal also contributes to change the orientation of these atoms.

It is an object of the invention to provide a resonant cell for optical pumping, which does not present those drawbacks.

According to a feature of the invention, the metal in solid state is contained in a portion of the cell building up a bulb formed in the wall of the cell and communicating with the latter through a bent portion. This bulb is, for example, arranged to be in symmetrical relationship to the pumping stem, with respect to the axis of symmetry of the body of the cell.

The invention will be best understood from the following description and appended drawing, wherein:

FIGS. 1 and 2 show, very diagrammatically, various embodiments of a vessel for resonance cells according to the invention.

The same reference numerals designate the same elements throughout all the figures.

Vessel 1 is provided with a pumping stem 2 for evacuating vessel 1 and introducing rare gas therein. A bulb 3, integral with vessel 1, is arranged for receiving metal 4 in solid state.

Referring to FIGS. 1 and 2, it may be seen that bulb 3 and the pumping stem 2 are positioned symmetrically with respect to the axis of vessel 1. In these figures, bulb 3 communicates with vessel 1 through a bent por- 3,242,423 Patented Mar. 22, 1966 tion 6 so that the metal in solid state 4 does not directly face the body of vessel 1.

In FIG. 2, the pumping stem 2 has also a bent portion 7 similar to that of bulb 3. The arrangement shown in FIGS. 1 and 2 makes it possible to avoid the disorientation of the atoms of the vaporized metal through collision with the solid metal 4, while a substantial amount of the latter can be placed in bulb 3.

The body of vessel 1 may be spherically shaped, which reduces the impacts of atoms against the walls. The number of these impacts is, as known, proportional to the surface of the body, whereas, for a given pressure, the number of the atoms is proportional to the volume of the body. In a sphere the ratio of the volume to the inner surface is a maximum; it follows that the coefiicient of disorientation through impacts against the walls is a minimum when vessel 1 has a spherical shape.

- The magnetic field applied may be, for example, perpendicular to the axis of the cell. The cell may then assume any desired position around an axis perpendicular to the magnetic field, without this resulting in any particular trouble as to the space required.

The described vessels are of course made of a material transparent to the light of the pump. They can contain a large amount of metal in solid state.

Of course, the invention is not limited to the embodiments shown which are given solely by way of example.

What is claimed is:

1. A resonance cell for optical pumping systems comprising in combination: a vacuum tight vessel having walls and including a main body, a bulb having a bent portion, formed in one of said walls and communicating with said body, and a pumping stem; and an alkali metal in said bulb and saturated vapour of this metal filling said vessel, whereby metal in the solid state in said bulb does not directly face said body.

2. A resonance cell for optical pumping systems comprising in combination: a vacuum tight vessel, having walls and an axis of symmetry, and including a main body, a bulb having a bent portion formed in one of said walls and communicating with said body, and a bent pumping stern; an alkali metal in said bulb and saturated vapour of this metal filling said vessel; said stern and said bulb being arranged symmetrically with respect to said axis, whereby metal in the solid state in said bulb does not directly face said body.

3. A resonance cell for optical pumping systems comprising in combination: a vacuum tight rotational vessel having a lateral wall and including a main body, a bulb having a bent portion, formed in said wall and communicating with said body, and a pumping stern; an alkali metal in said bulb and saturated vapour of this metal filling said vessel, whereby metal in the solid state in said bulb does not directly face said body.

References Cited by the Examiner UNITED STATES PATENTS 2,884,524 4/1959 Dicke 324-0.5 3,038,126 6/1962 Robinson 3240.5

FOREIGN PATENTS 1,215,432 11/1959 France.

875,242 8/ 1961 Great Britain.

(Other references on following page) 3 OTHER REFERENCES Carpenter et al.: Physical Review, vol. 46, October 1934, pp. 607 to 612.

De Zafra: American Journal of Physics, vol. 28, No. 7, October 1960, pp. 646 to 654 incl.

Franzen: Physical Review, vol. 115, No. 4, Aug. 15, 1949, pages 850 to 856 inclusive.

Kastler: The Ann Arbor Conference on Optical PumpingUniversity of Michigan, Ann Arbor, Michigan, June 1959, pp. 71-73 principally relied on.

4 Novick: Ann Arbor Conference on Optical Pumping, pages 11 to 16 relied on.

Ritter et 211.: Royal Society of London, Proceedings, vol. 238, N0. 1215, Jan. 29, 1957, pp. 473 to 488 (pp. 477479 principally relied on).

CHESTER L. JUSTUS, Primary Examiner.

MAYNARD R. WILBUR, Examiner. 

1. A RESONANCE CELL FOR OPTICAL PUMPING SYSTEMS COMPRISING IN COMBINATION; A VACUUM TIGHT VESSEL HAVING WALLS AND INCLUDING A MAIN BODY, A BULB HAVING A BENT PORTION, FORMED IN ONE OF SAID WALLS AND COMMUNICATING WITH SAID BODY, AND A PUMPING STEM; AND AN ALKALI METAL IN SAID BULB AND SATURATED VAPOUR OF THIS METAL FILLING SAID VESSEL, WHEREBY METAL IN THE SOLID STATE IN SAID BULB DOES NOT DIRECTLY FACE SAID BODY. 